Iridium(III) Blue Phosphors with Heteroleptic Carbene Cyclometalates: Isomerization, Emission Tuning, and OLED Fabrications

Ir(III) complexes are particularly noted for their excellent photophysical properties in giving blue OLED phosphors. In this study, two distinctive carbene pro‐chelates LAH2+ and LBH2+ (or LCH2+) were employed in preparation of heteroleptic Ir(III) complexes, to which LAH2+ bears a cyano substituted benzoimidazolium along with N‐mesityl appendage, while LBH2+ (or LCH2+) carries the symmetrical benzoimidazolium entity. Notably, the reversible equilibration at high temperature was observed for m, f‐ct14 and m, f‐ct15 with a single LA chelate. In contrast, only the mer‐substituted m‐ct16 was obtained upon employing two LA chelates. All Ir(III) complexes exhibited blue photoluminescence (ΦPL ≥ 78%) with short radiative lifetimes (τrad ≤ 1.05 µs) in solution. The Ph OLED device with m‐ct16 afforded an external quantum efficiency (EQE) of 22.8% at 5000 cd m‒2. Moreover, the hyper‐OLED based on m‐ct16 and v‐DABNA exhibited EQE1000 of 32.1% (EQE recorded at 1000 cd·m−2) and J90 of 15.0 mA cm‒2 (current density at 90% of max. EQE). Its suppressed efficiency roll‐off (EQE of 32.1% and 27.7% at 1000 cd·m‒2 and 10000 cd·m‒2) demonstrated a milestone in fabrication of blue OLED devices.